VIENNA: Iran is set to be the main talking point at a two-day meeting of the UN atomic agency starting Thursday, amid ongoing weaponisation fears and safety concerns over Tehran's only operating nuclear power plant.

Western countries will refrain however from seeking a censure motion from the 35-nation International Atomic Energy Agency board against Iran, in part to enable renewed diplomatic efforts to resolve the long-running crisis a chance.

In September, 31 countries backed a resolution of "serious concern that Iran continues to defy" UN Security Council resolutions for it to suspend its uranium enrichment, which can be used for peaceful means but also for a nuclear weapon.

The IAEA'S latest report on Iran on November 16 said that while diplomatic efforts have been deadlocked for the past six months, Tehran has been using the time to steadily expand its activities.

Iran is ready to switch on another 696 centrifuges at Fordo, enabling it to double production of 20-percent enriched uranium at the heavily fortified facility, the report said.

Fordo's final 644 machines have also been installed but are not yet ready to be put into operation. Once they are, Iran will be able to triple its current monthly output of 20-percent enriched uranium to some 45 kilos (100 pounds).

The Fordo complex is a key site in Iran's nuclear programme, dug deep into a mountain to protect it against air strikes.

Israel, which has refused to rule out military action, is thought to have a "red line"; when Iran has produced around 250 kilos. That would be enough, if further enriched, for one nuclear weapon.

Supporting Iran's argument that its programme is for peaceful means is the IAEA's finding that of the 232.8 kilos of enriched uranium produced so far, 96.3 kilos has been converted into a powder that can then be turned into fuel for a reactor producing nuclear medicine.

The amount converted has however slowed dramatically, indicating possible technical problems, and once Fordo is fully up and running, Iran will be producing far more material than its civilian facilities need, experts say.

The IAEA's report also said that Iran, the only country with an operating nuclear reactor that does not adhere to the post-Chernobyl Convention on Nuclear Safety, has unloaded fuel at the Bushehr plant, shutting it down.

Iran's envoy to the IAEA, Ali Asghar Soltanieh, told AFP that the move was a "normal technical procedure" but Western diplomats said it raised fresh questions about safety at the 1,000-megawatt facility on the Gulf coast.

"This is not a routine matter or something that is ordinary. This is a matter of great concern," one senior Western official said.

The reactor, started by Germany's Siemens and completed by Russian firm Rosatom, was only plugged into the nation grid in late 2011 after years of financial, technical and political delays.

This latest suspected problem "is probably not something to be overly worried about, either on proliferation or safety grounds," said Mark Fitzpatrick from the International Institute for Strategic Studies in London.

"But because of the way Iran does this, without giving any details, it naturally creates concerns," Fitzpatrick told AFP last week.

The IAEA and Iran talks are set to resume on December 13 in Tehran, meanwhile, focused on what the agency calls "overall, credible" evidence that until 2003, and possibly since, Iran conducted nuclear weapons research.